There has been much chatter about the threat of an asteroid or significant meteor strike on Earth in the past few weeks - mostly caused by the untracked meteor that blasted its way to international attention when it exploded in the sky above Russia injuring nearly 1,200 people in February.
It was one of those amazing coincidences that on that same day an asteroid NASA had been tracking for months -- asteroid 2012 DA14 - was to harmlessly cross Earth's path.
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The events of that day in particular play up the difficulty of tracking such objects. It also demonstrated the significance or perhaps insignificance of spending tons of money and developing new technologies to tracking such objects.
Those events and the topic of mitigating asteroid and meteor or Near Earth Object threats to Earth prompted a couple congressional hearings by the Committee on Science, Space, and Technology, the latest of which was held this week.
"Because it was found a year in advance, we were able to accurately predict the close Earth passage of asteroid 2012 DA14 on February 15, and we knew that it would not hit the Earth. However, the small asteroid that impacted the Earth's atmosphere over Russia arrived unannounced because it came from the direction of the Sun, and was hence unobservable with Earth-based telescopes. Discovering and identifying relatively small Earth impactors among the millions of asteroids in the Earth's neighborhood represents a significant challenge. Because there are so many more smaller asteroids than larger ones, the smaller ones hit the Earth's atmosphere more frequently. There are about ten million 20-meter sized asteroids like the one that exploded over central Russia two months ago, and their frequency of collision with the Earth is about once every 100 years, on average," Donald Yeomans, manager of the Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory.
Yeomans went on to say that the NASA-supported NEO observations program is proceeding extremely well, and the rate with which NEOs are being discovered and physically characterized is increasing each year.
"[In] 2007, about 80% of the NEOs one kilometer or larger had been discovered and only a few percent of the smaller 140 meter objects. Today, the Spaceguard goal of discovering 90% of the large NEOs has been exceeded and about 25% of the 140 meter or larger sized NEO population has been discovered. Today, the discovery rate of NEOs is about 1000 per year, up 50% since 2007. The Minor Planet Center in Cambridge, Massachusetts, has 100 million observations of NEOs in its database and 27,000 observations are added daily. Fully 96% of all NEOs were discovered by NASA-funded surveys," he stated. Still there is still much work to be done. About 50-100 NEOs larger than one kilometer remain undiscovered, along with about 13,000 NEOs larger than 140 meters and millions of objects larger than about 30 meters in extent - the approximate minimum size for a common stony asteroid to cause significant ground damage.
"None of the NEOs found to date have more than a tiny chance of hitting Earth in the next century. Thus the near-term risk of an unwarned impact from large asteroids, and hence the majority of the risk from all NEOs, has been reduced by more than 90%. Assuming none are found to be an impact threat, discovering 90% of the 140 meter sized objects will further reduce the total risk to the 99% level. By finding these objects early enough and tracking their motions over the next 100 years, even those rare objects that might be found threatening could be deflected using existing technologies. For example, a spacecraft could purposely ram the asteroid, modifying its orbital velocity by a very small amount, so that over several years its trajectory would be modified and its predicted impact of Earth in the future avoided by a safe margin," Yeomans said.
There are viable options for accelerating the current NEO search efficiencies either using next-generation, ground-based optical surveys or the even more efficient space-based infrared surveys.
Yeomans detailed some future technologies that will help with space objection identification.